User manual BENDIX M-21-M-22 ANTILOCK MOD ASSY

[. . . ] Brake application air enters the supply port of the modulator and flows to, and through, the open exhaust solenoid then to the exhaust diaphragm. Air pressure, along with spring force, seats the exhaust diaphragm on the exhaust passage thus preventing the escape of service air. Simultaneously, application air flows to the supply diaphragm and forces it away from its seat. Air flows past the open supply and out the modulator delivery port to the service brake chambers. 2 EXHAUST DIAPHRAGM EXHAUST SOLENOID EXHAUST PORT BRAKE VALVE SUPPLY SOLENOID SPRING BRAKE CHAMBER SUPPLY DIAPHRAGM SPRING FIGURE 3 - M-21TM, M-22TM MODULATOR NON-ANTILOCK APPLICATION OF SERVICE BRAKES EXHAUST DIAPHRAGM EXHAUST SOLENOID EXHAUST PORT BRAKE VALVE SUPPLY SOLENOID SPRING BRAKE CHAMBER SUPPLY DIAPHRAGM SPRING FIGURE 4 - M-21TM, M-22TM MODULATOR NON-ANTILOCK APPLICATION HELD POSITION 3 EXHAUST DIAPHRAGM EXHAUST SOLENOID EXHAUST PORT BRAKE VALVE SUPPLY SOLENOID SPRING BRAKE CHAMBER SUPPLY DIAPHRAGM SPRING FIGURE 5 - M-21TM, M-22TM MODULATOR NON-ANTILOCK EXHAUST OF SERVICE BRAKES (NORMAL) NON-ANTILOCK EXHAUST The manner in which air exhausts through the modulator differs, depending upon how rapidly the brake application is released by the driver. [. . . ] Air pressure acting on the supply diaphragm causes it to close the supply and prevent further delivery of air to the brake chamber. Energizing the exhaust solenoid closes its inlet and opens its exhaust. By closing the exhaust solenoid inlet, application air is prevented from flowing to the control side of the exhaust diaphragm. Air pressure, which was present on the control side of the exhaust diaphragm flows out the exhaust port of the modulator. With control air pressure removed from the exhaust diaphragm, brake application air forces the exhaust diaphragm to unseat which allows it to flow out the modulator exhaust port. The modulator will remain in the antilock exhaust mode until the antilock controller senses that wheel speed has increased. The modulator can enter the antilock hold or re-apply mode from the antilock exhaust mode. ANTILOCK HOLD The antilock controller will place the modulator in the hold position when it senses that the correct wheel speed (braking force) has been attained. The antilock controller will also place the modulator in the hold position, prior to entering the re-apply, when it detects recovery from a locked wheel condition. In this mode of operation the modulator supply solenoid remains energized while the exhaust solenoid is de-energized. De-energizing the exhaust solenoid opens its inlet and closes its exhaust. Opening the exhaust solenoid inlet, allows application air to flow to the control side of the exhaust diaphragm which then seals the exhaust passage. With the exhaust diaphragm seated, further exhaust of brake chamber air pressure is prevented. Because the supply solenoid remains energized the supply diaphragm remains seated, thus preventing application air from flowing to the delivery port and out to the brake chamber. The modulator can enter the antilock exhaust or re-apply mode from the antilock hold mode. 5 EXHAUST DIAPHRAGM EXHAUST SOLENOID EXHAUST PORT BRAKE VALVE SUPPLY SOLENOID SPRING BRAKE CHAMBER SUPPLY DIAPHRAGM SPRING FIGURE 7 - M-21TM, M-22TM MODULATOR ANTILOCK EXHAUST OF BRAKES ANTILOCK RE-APPLY If the antilock controller senses that wheel speed has increased sufficiently to require reapplication of braking pressure, it de-energizes the supply and exhaust solenoids. With both solenoids de-energized, the modulator re-applies air to the brakes in the same manner it did during a nonantilock application. 3. Test air line fittings for excessive leakage and tighten or replace as necessary. Perform the ROUTINE OPERATION AND LEAKAGE TESTING described in this manual. OPERATION & LEAKAGE TESTS LEAKAGE TESTING 1. Turn the engine OFF and make 4 or 5 brake applications and note that the service brakes apply and release promptly. If leakage exceeds the specified maximum, tighten the solenoid cap screws and re-test. If the leakage remains excessive after re-testing, replace the modulator. PREVENTIVE MAINTENANCE GENERAL Perform the tests and inspections presented at the prescribed intervals. If the modulator fails to function as described, or leakage is excessive, it should be replaced with a new or genuine Bendix remanufactured unit, available at any authorized parts outlet. EVERY 3 MONTHS, 25, 000 MILES OR 900 OPERATING HOURS 1. Remove any accumulated contaminates and visually inspect the exterior for excessive corrosion and physical damage. [. . . ] If the work is being performed on the vehicle's air brake system, or any auxiliary pressurized air systems, make certain to drain the air pressure from all reservoirs before beginning ANY work on the vehicle. If the vehicle is equipped with an AD-ISTM air dryer system or a dryer reservoir module, be sure to drain the purge reservoir. Following the vehicle manufacturer's recommended procedures, deactivate the electrical system in a manner that safely removes all electrical power from the vehicle. Never connect or disconnect a hose or line containing pressure; it may whip. [. . . ]